Transitional Whale Species Hunted at Sea, Gave Birth on Land

Early whales hunted at sea but spent the rest of their time on land, suggest two newly-described fossil whales — one of them a pregnant female — believed to represent a transitional species between earth- and water-bound behemoths.

Dating from 47.5 million years ago, the whales had large teeth suited for consuming fish, and flipper-like limbs that could support their weight on land, albeit awkwardly. The fetal skeleton was positioned for head-first delivery, typically seen in land mammals. Modern whales give birth tail-first.

"They clearly were tied to the shore," said study co-author Philip Gingerich, a University of Michigan paleontologist, in a press release. "They were living at the land-sea interface and going back and forth."

"About 40 to 50 million years ago, the ocean was very rich with life, fish and other creatures, in shallow water," said Brian Huber, a Smithsonian Institute paleontologist, during the opening of an M. inuus-featuring exhibit last fall. "Mammals were diversifying on land, and there was a lot of competition for food. So, some mammals began living part of their lives in the ocean, just to feed. At some point, they began living all of their lives in the ocean."